Yes, it’s supposed to work - with a caveat that it won’t work if you plug it in very slowly (a detection is triggered by insertion event, but if you plug it in slowly headphones may get detected already before microphone ring makes contact), and it won’t work if you have a switch that disables the microphone on your headset engaged (you’ll have to unplug and plug it back in with it disengaged for it to be detected).
Definitely not a slowness of insertion issue. Validated that my librem5-base package is in tack(dpkg --verify librem5-base). Any way to test to see if it’s a hardware issue? Don’t think I’ve ever had a computer’s headphone jack fail partially before.
If not I’ll reach out to support. Feel bad poking them as I expect they are swamped with new user questions/issues right now.
You may also want to make sure that the headset you’re plugging in uses AHJ/CTIA TRRS standard (with mic at the sleeve). Librem 5 does not support the less common OMTP standard (with ground at the sleeve), so for those headsets you’d need an adapter. Apparently Apple had its own incompatible connection system too - something to keep in mind.
Headset mics work fine for me. When I use a splitter to connect to my car stereo and a wired mic, it stopped working a few months ago. Used to work fine. Verified this with multiple cable/splitter/mic sets.